Venetian blinds are well-known window coverings. They have a series of horizontal slats hung from ladders which extend between a headrail and a bottomrail. The slats can be rotated between an open, see through position and a closed position. Additionally, the blinds can be raised and lowered. Venetian blinds contain aluminum, plastic, fabric or wood slats and are available in a wide range of colors.
Another type of window covering, called a vertical blind, has a series of vertical vanes that travel on an overhead track. The vanes can be rotated in much the same way that the slats of a venetian blind are rotated. Some vertical blinds also have a panel of fabric through which light may pass that is attached to one edge of the vanes. The fabric will extend over the window when the vanes have fully traversed the overhead track. Typically, the fabric is a sheer or open weave material which allows light to pass. A second panel of fabric may be attached to the opposite edge of the vanes.
Fabric window coverings and draperies are often preferred by consumers over venetian blinds and vertical blinds because they have a softer, warmer appearance. However, draperies do not have the ability to control the amount of light transmitted through the window covering in a manner similar to louvered blinds like the traditional venetian blind and vertical blind.
Several attempts have been made to provide a fabric window covering with the ability to control the amount of light entering the room. Shapiro in U.S. Pat. No. 3,851,699 discloses a window draw drape having spaced apart light impeding and light transmitting vertical sections. The light impeding sections can be rotated to cover all or portions of the light admitting sections. The light impeding sections are vertical slats attached to the drapery or tightly woven fabric. The light admitting sections are open mesh. This product is difficult to operate because the light impeding sections tend not to align with the light admitting portions when those sections are rotated.
In U.S. Pat. No. 5,313,999 to Colson et al. there is a window covering having first and second parallel sheer fabric sides and a plurality of light impeding or somewhat light impeding vanes extending between the sheer fabric sides. The vanes are angularly controllable by relative movement of the sheer fabric sides. Like the combination of a sheer fabric and a light impeding fabric this system allows the user to have a fully open window, a sheer covered window allowing light transmission with day time privacy, and a more opaque covering providing night time privacy or room darkening. In addition, it the has intermediate light control of a louvered product like venetian blinds. The Colson window covering system is difficult to manufacture and to fabricate, has a limited range of fabrics it can use, and has a very flat appearance when in the light impeding mode. Another problem with this window covering is that a moire appearance often occurs on the front face of the window covering as a result of an alignment between the weave pattern of the front sheet and the weave pattern of the rear sheet. When this window covering is attached to a roller, the material tends to crumple or wrinkle when rolled up. The material is also hard to cut and the cut edges are difficult to seal because of the sheer fabrics that must be used.
Another light control window covering system is disclosed in U.S. Pat. No. 3,384,519 to Froget. The window covering disclosed there consists of two cloth layers spaced apart by movable parallel blades having each of their marginal edges heat welded to one of the movable cloth layers. Froget's welding uses the material present which is very thin in order to be see-through, flexible, and store well. It is difficult to precisely apply heat and pressure to sufficiently bond these layers without damaging them by melting through the layer or forming warp spots. With this window covering relative movement of the two cloth layers in a direction perpendicular to the blades changes the angle of the blade and thus controls the amount of light passing through the article. Because the blades must be heat welded to the cloth layers, only thermoplastic materials can be used. Also, heat welding necessarily requires a melting of some of the fibers of the material bonded, thus providing an uneven outer appearance along the heat welds and producing unwanted crimps or creases of the material which can result in fatigue failure. Furthermore, heat welding is a relatively slow process and the resulting weld is limited in strength. The window covering material in the Colson and Froget blinds is tilted and stored on a roller wrapping successively around itself. When the layer is displayed over the window the front layer is the same length as the back layer. When the layers are stored around the roller each layer travels a progressively larger or longer path, the difference depending on the thickness of each fabric. Since all the layers are bonded together the wrapping can cause wrinkling on the layers traveling on the inside or shorter paths. Having very uniformly thin layers helps mitigate this problem, but requiring thin layers limits the variations of the weave, yarns, style and other fabric features that can be chosen.
In my U.S. Pat. No. 5,339,882, I disclose a window covering having a series of slats connected between two spaced apart sheets of material. The slats are substantially perpendicular to the sheets of material when the covering is in an open position. The slats are substantially parallel to the first and second sheets of material when the window covering is in a closed position. This product has many of the same limitations of the window covering disclosed by Colson and Froget. All these products use sheets of fabric and have all the problems associated with fabric sheets.
In U.S. Pat. No. 5,753,338 Jelic et al. disclose a honeycomb material for window coverings in which the front face, back face and slats are interwoven simultaneously. This process uses an improved warp knitting technique in which a front mesh and a rear mesh are provided and warp threads are woven through them. The two meshes are maintained parallel to one another. At selected intervals slats are woven between the two meshes to form a honeycomb structure. Since the warp threads weave back and forth between meshes, it would seem almost impossible for the slat to have a greater density than the “faces.” Secondly, since the material is created with the slats being perpendicular to the meshes, the slats must bend to affect the closure, but they have no hinge portion. This window covering has not been commercialized, but one would expect it to have the same problems as the window covering disclosed by Colson.
A problem with these fabric structures is that they must be very precisely made to look and function properly. But, textiles are inherently inconsistent and unprecise due to the nature of the weaving, printing and coating processes. Changes in temperature and humidity cause fabric to expand and contract. If a sheet of fabric is hung between a headrail and a bottomrail, a change in temperature or humidity may cause the edges of the fabric to move inward. Such movement is severely restrained near the headrail and the bottomrail, but can more easily occur around the center of the fabric. Consequently, the fabric sheet will assume an hourglass shape. For many fabrics this hourglass appearance is quite noticeable, particularly for longer shades. One way in which the art has been able to address this problem is to avoid using many fabrics for window coverings that will be subject to wide ranges of temperature and humidity. Some fabrics can be coated with starch or other chemicals to prevent shrinkage. But, that treatment increases costs.
There is a need for a window covering system which provides the light control of a venetian blind and a vertical blind with the soft appearance of draperies and pleated shades. This window covering should be available in a wide variety of fabric, colors and styles. The window covering should not be adversely affected by changes in temperature and humidity. The window covering should be able to be easily cut down from standard sizes and to be otherwise easy to fabricate. The system should be simple to install and to operate and able to be manufactured at a cost which allows the product to be sold at a competitive price. Furthermore, the window covering should not suffer from the moire effect that has plagued the window coverings which have two parallel sheets of light transmissive material. Finally, the window covering should be easy to clean and maintain.